Current high throughput screening (HTS) assays typically only include one cell type with limited metabolic competence. Therefore, drugs and chemicals that are naturally metabolized by liver hepatocytes or other cell types into active compounds or become quickly detoxified generate false-negative and false-positive results, respectively. Existing co-culture or multi-culture devices are expensive and are poorly suited to higher density 96, 384 and 1536 well microtiter plates. A simple co-culture platform would greatly improve the accuracy of the HTS assays.